Windows 11 does not install without Secure Boot and a TPM 2.0, and the new
VM form offered neither: its firmware list was BIOS and one UEFI loader
guessed from file names, which on RHEL never matched the Secure Boot one.
The firmware choices are now BIOS, UEFI and UEFI Secure Boot, as the
host's libvirt reports them (its firmware features from libvirt 12.1,
before that its loaders), and libvirt picks the firmware itself: UEFI
without Secure Boot, or with Microsoft's keys enrolled. A TPM 2.0 switch,
shown when the host has swtpm, adds an emulated TPM. The create job
refuses a firmware or a TPM the host does not offer, and the API takes
both. The path-guessing helpers are gone.
An existing q35 VM whose PCIe root ports are all used takes no new
virtio disk or network device while it runs, and the only way to give
it more was editing its XML.
The Disks tab of a PCIe machine now counts its slots, "PCIe slots: 0
free of 7", in red when none is free, with what its next start will
have when that differs, and Add PCIe slots adds four root ports to its
persistent definition: libvirt numbers and places them, and a running
VM gets them at its next start. The no-slot advice of Add disk and Add
network device points at it.
On a q35 machine each PCIe device (a virtio disk, a network card) takes
a root port of its own, libvirt makes only as many ports as the VM is
defined with, and a running VM gets no new one: adding a virtio disk to
such a VM failed with libvirt's "No more available PCI slots".
A new q35 VM is now defined with the PCIe root and 14 root ports, as
virt-install makes them: libvirt puts the VM's devices into them and
leaves the rest free for devices added while it runs.
When a running VM has no free slot, Add disk and Add network device say
what to do instead of libvirt's words: for a disk, the scsi bus when
the VM has a SCSI controller (its disks need no slot of their own), or
adding it with the VM shut down, where libvirt makes the port; for a
network device, shutting the VM down. A new volume whose attach was
refused stays in its pool, as before, to attach as an existing volume.
